Coronary artery disease is the leading cause of death in the U.S. Tests are urgently needed that can detect and distinguish vulnerable plaque formation so that they may be treated before a catastrophic event. Angiography is a useful tool for assessment of stenoses, and contrast agents that could be administered non-invasively and visualize composition as well as morphology should be developed. Nanoprobes, Inc. has combined nanotechnology with this medical application and developed the use of tiny nanoparticles as x-ray contrast agents. These have a number of advantages over the current iodine compounds: they provide longer imaging times, have lower osmolality to reduce side effects, are higher in atomic number so that the dose of x-rays can be reduced, and can be concentrated more than iodine agents. Preliminary imaging in mice revealed 0.2 mm vessels and visualization of many internal organs with great clarity not possible with the current contrast agents. Phase I will concentrate on and comparing the performance of the new agents with the iodine agents, quantifying their properties, and measuring acute and subacute toxicity. A further objective of this work to be explored in Phase II is the development of targeted contrast agents that would be able to discriminate high-risk atherosclerotic plaques.